Is my HDD completely dead?

WD5000AAKS 500GB ~3.5 years old

It works fine last night ~10 hours ago. Several days before though, it would keep saying "error loading operating system" from time to time. I would have to press reset button, and it would boot fine.

Right now, BIOS load fine but shows blank on where HD should be. When it tries to boot OS, it stalls for about 20 sec before it tries to boot from CD

I tried putting in win7 OS cd to format it, but it did not detect any HDD.

I put the HD my brother's PC by itself, and it stalls with blinking cursor on top left on screen. Also tried using 'detect HD' feature in BIOS, but still shows blank.

Then I put the HD in together with working HD, same thing. I even try to boot the OS exclusively from the working HD and it still stalls.

Any ideas?

Specs:

Intel Core i7 920 @ 4.00Ghz
EVGA 3-way SLI E758-A1
OCZ 1000W ProXStream
OCZ Platinum 6GB (3x2GB)
CM HAF 922
BenQ 24" FP241VW
GeForce 8800 GTX
Win7 Home x64